SharePoint Columns Not Appearing in Power BI Dataset

I am a new user of Power BI but I can pretty much build simple dashboards.

I created a SharePoint list which gets updated by a Power App I also built. In my SharePoint list, I have a column for the employee name taken from another SharePoint list (Active Employees). This allowed me to include additional columns such as the employee ID, line of business, location, and supervisor name.

Thus, when I add a new entry in the list either through the Power App or directly on the list, entering just the agent name already pre-populates the employee ID, line of business, location, and supervisor name on the list item.

When I click on Export to Power BI the dataset only includes the agent name but not the employee ID, line of business, location, and supervisor name.

However, the Export to Excel option shows those details.

I wanted to do reports based on line of business, location, and supervisor, but these columns are showing up empty in Power BI. They are perfectly fine in Excel.

Here are my questions:

1. What is wrong with the Power BI data set that it leaves all other columns empty?
2. What can be done in this case?
3. If I were to add a new column to my SharePoint list, how does that new column get added to my dataset since I already created a Power BI report out of that data set?

Appreciate the help, thanks in advance!